The present invention relates in general to wire coiling machines, and pertains more particularly, to a machine for coiling wire with an improved wire feed, preferably sinusoidally varying in feed speed, with intermittent feed interruption for cutting.
Various types of wire coiling machines are generally known in the art. By way of example, U.S. Pat. No. 1,266,070 to Sleeper and U.S. Pat. No. 2,175,426 to Blount et al show were feed rollers that are in constant engagement with the wire but driven intermittently by means of a reciprocable gear segment of a variable throw. One of the problems with that construction was an appreciable loss of time in the necessity for returning the gear segment to its starting position at the same speed at its forward motion. By way of another example such as shown in U.S. Pat. No. 1,452,128 to Sleeper and U.S. Pat. No. 2,096,065 to Blount the wire feed rollers are driven through a clutch which is controlled by a cam mechanism arranged to stop the feed periodically for the wire cutting operation.
Generally speaking, there are two basic techniques that are presently employed for interrupting wire feed to accomplish the cutting of the wire after the spring has been formed. One technique controls the feed rollers so that they are stopped and motionless at the time of cutting. There is typically about a 120.degree. dwell time thus providing only a 2/3 duty cycle. This is time consuming and limits the number of springs that can be formed per minute.
Another present machine causes a lifting of one of the feed rollers to thus stop wire motion. However, this machine is provided with a constant speed drive of the feed rollers. In order to provide a suitable speed of production of springs, the feed rollers are driven at a constant speed that has now been found to create certain problems. Particularly, when the feed rollers are re-engaged there is a tendency for the wire to become distorted. Because of this re-engagement at full constant speed there is generally required a large pressure on the rollers to compensate for this high speed start. As previously mentioned, this creates wire distortion especially when coiling larger gage wires particularly in small coils. The wire distortion includes distortion of both pitch and diameter accuracy.
Accordingly, it is an object of the present invention to overcome the aforementioned disadvantages associated with prior art machines by providing a variable speed drive which enables a high duty cycle of operation and which also enables start-up at reduced speed so as to minimize wire distortion.
Another object of the present invention is to provide an improved wire coiling machine particularly characterized by an improved wire feed apparatus combining variable speed feed with intermittent feed interruption for cutting. The variable speed feed, preferably of sinusoidal type, varies between a maximum speed essentially at the midpoint of the coiling operation to a minimum speed at feed interruption. In the disclosed embodiment a pair of elliptical gears are used for the variable speed drive, although other means may be provided such as the use of other non-circular type gears.
Another object of the present invention is to provide a wire coiling machine characterized by improved accuracy in production in cutting of the coil spring.